Thermoplastic elastomers do not require a vulcanization process and can be processed by a molding machine for processing an ordinary thermoplastic resin. These characteristics are being harnessed to use thermoplastic elastomers in a broad range of fields, including automobile parts, home electric appliances or other miscellaneous goods. Among thermoplastic elastomers, an olefinic thermoplastic elastomer obtained by kneading an olefin copolymer rubber obtained by polymerizing ethylene, an α-olefin having 3 to 20 carbon atoms and a non-conjugated polyene, with an olefin resin, is widely used as a material that is light weight, recyclable, chlorine-free and environmentally friendly.
Known production methods of olefinic thermoplastic elastomers include kneading an olefin copolymer rubber and an olefin resin in a closed mixer as exemplified by a Banbury mixer. However, because a batch kneader such as a Banbury mixer is used, this method suffers from the problem of having poor productivity and being inefficient.
A method known for resolving this problem is to knead the olefin copolymer rubber and olefin resin with a twin-screw extruder. For example, JP-A-2006-37115 describes a method for producing a rubber composition in which a rubber mixture comprising 100 parts by weight of an olefin copolymer rubber and 3 to 10 parts by weight of a volatile organic solvent are charged into an extruder from the supply port of a multistage vented extruder; a polyolefin resin is charged into the extruder from another supply port under an inert gas atmosphere; the rubber mixture and the polyolefin resin are kneaded; and the solvent is removed.